1. Field of the Invention
This invention relates to a method and apparatus for performing differential thermal analysis as well as dynamic mechanical analysis of a sample relative to a reference.
2. Brief Description of the Prior Art
In the case of differential thermal analyses, for example, the temperature is regulated, raised, lowered, or kept isothermal in a furnace. In addition to the sample to be measured, the furnace contains a reference or comparison sample whose temperature behavior is known. The material of the reference sample as a rule does not contain any anomalies in the temperature measurement that is of interest here. Above all aluminum oxide or the empty sample pan or receptacle is customary and suitable for use as a reference material. The difference derived from the sample temperature and the reference temperature is a measure of the heat flow change of the sample. The technique of thermal analyses, especially also the technique of differential thermal analyses and dilatometric analysis techniques, is described in a comprehensive fashion in the text book entitled "Methoden der Thermischen Analyse" [Methods of Thermal Analysis], W. F. Hemminger, H. K. Cammenga, Springer Publishers 1989, from the series entitled "Guidelines for Chemical Laboratory Practice"; the content of this text book is thus included by reference in the instant specification. The technique of dynamic mechanical analysis (DMA) is disclosed in the publication Thermal Analysis, by Bernhard Wunderlich, Academic Press, Inc., pages 350-357.
If the reference sample and the sample to be measured are simultaneously placed in the furnace then--even in case of the best analysis instruments, made with maximum precision--there are certain nonhomogeneities and differences not only in the heat and temperature fields but also in the material of those instruments themselves. The reference sample and the sample to be measured are located in different places in the furnace; in other words, they are exposed to a non-completely homogeneous temperature field in different places.
Moreover, the reference sample and the sample to be measured influence each other. That is a disturbing factor above all because this influences greatest, of all things, in the particular interesting temperature range or time frame, where the sample to be measured, on the basis of the exothermal or endothermal processes, shows deviations in the sample to be measured from the reference sample.
The sample carrier, for example, the pan carrier or the pan itself, not only for the reference and for the sample to be measured, but also the measurement sensors themselves, always show minor differences. This leads to small although always disturbing influences on the measurement results and adulteration of the results.
If an analysis apparatus is to be used to determine not only a single material property but also various different material properties, in other words, if, in addition to differential thermal analysis, for example, one also determines dilatometric properties, in other words, if one performs a thermal-mechanical analysis (TMA) or a dynamic-mechanical analysis (DMA) of the sample to be measured, then the result of the differential thermal analysis can be additionally influenced in a negative manner by the expanded measurement arrangement for the determination of these additional material properties in the sample to be measured.